It is well known to supply a liquid composition, through a fine-structure channel, to a liquid chamber provided with an energy-producing means such as a piezoelectric element, resistance heater or the like and pressurize the liquid composition thus supplied under an energy produced by the energy-producing means for spraying as droplets from a spray nozzle provided at the liquid chamber.
As a typical one of the conventional liquid spraying apparatuses, an ink-jet printer is known in which ink is sprayed from head tips to, for example, recording paper as an object to form graphics and/or characters on the paper.
The ink-jet printer is advantageous because of its low running cost, compact design and easy printing of an image in colors. In the ink-jet printer, ink of colors such as yellow, magenta, cyan, black and others is supplied from ink cartridges filled with the respective ink to an ink chamber or the like in each of the head tips.
In the ink jet printer, ink supplied to the ink chamber or the like is pressurized in the ink chamber by a pressure-producing element such as a resistance heater or the like provided in the ink chamber for spraying from tiny holes, namely, so-called nozzles, formed in each head tip. More particularly, the ink in the ink chamber is heated by the resistance heater provided in the ink chamber to produce bubbles in the ink on the resistance heater, and the ink is sprayed from the nozzles under a pressure produced when the bubbles break up and disappear for projection onto recording paper or the like to form graphics and/or characters on the paper.
In the printer of this ink jet type, the performance of ink spraying from the nozzles of the head tips has a large influence on the quality of images formed on the paper. Therefore, head tips that can be produced with an improved precision, such as head tips each formed form a wafer of silicon or silicon oxide, for example, and having a resistance heater embedded therein, have become marked.
More particularly, such head tips include head tips built by forming a resistance heater on a silicon wafer and each of which uses the end face of the silicon wafer as a channel for guiding ink to the ink chamber.
In such a head tip, the surface of the silicon wafer on which the resistance heater is formed is oxidized so that the silicon or silicon oxide will not be eluted into the ink even if it is exposed to the ink. However, the process of production will make it difficult to oxidize the end face of the silicon wafer and the silicon or silicon oxide will be eluted into the ink if it is exposed to the ink as the case may be. Especially in the case of alkaline ink whose pH is higher than 7, silicon will heavily be eluted from the silicon wafer into the ink. It should be noted that most of the ink for printing to paper are alkalescent in order to prevent metallic portions of the head tips from being oxidized.
If the metallic portions of the had tip are so oxidized, melting of the silicon wafer will lower the dimensional accuracy of the head tips, leading to deterioration of the ink spraying performance, quality deterioration of images formed on the paper, non-spraying of the ink and other troubles as the case may be.
Also, the silicon elution from the silicon wafer will lower the bonding strength at the junction between the silicon wafer and other parts joined to the silicon wafer, so that the other parts will be separated from the silicon wafer, which will possibly damage the head tips.
In case the ink chamber and channel are formed from the silicon wafer, such silicon elution from the silicon wafer will lower the dimensional accuracy of the chamber and channel, possibly resulting in deterioration of the spraying performance of the had tip.
In the ink having the silicon or silicon oxide eluted therein, the stability of dye dispersion is lost so that the dye will possibly deposit and clog the nozzle.
As the ink solvent evaporates, the silicon or silicon oxide eluted in the ink will cause super-saturation of the ink and deposit in the ink and clog the nozzle to possibly cause non-spraying of the ink.
Also, the silicon or silicon oxide eluted in the ink will have the solubility thereof increased in the ink heated around the resistance heater and will thus melt excessively in the ink, and deposit on the resistance heater due to rapid cooling after the ink is sprayed. Namely, the elution of the silicon or silicon oxide will possibly cause the so-called “cogation”. In the head tip in which the “cogation” has thus occurred on the resistance heater, it will be difficult to heat the ink appropriately, causing the non-spraying of the ink.
To solve the above-mentioned problems of the conventional techniques, it has been proposed to design a head tip structure in which the silicon wafer will not be exposed to the ink or making surface treatment of the silicon wafer to prevent the silicon or silicon oxide from being eluted from the silicon wafer. More specifically, it is proposed in the Japanese Patent Application Laid Open No. 85949 of 1997 to provide a layer of SiN, TiN, TiO or the like on the surface of the silicon wafer, for example.
The above proposals permit to prevent the silicon or silicon oxide from being eluted from the silicon wafer into the ink, but they are not advantageous in that the number of steps of producing the head tips is increased, resulting in an increased manufacturing cost and lower yield. The printer product including the head tips will be very expensive. Also, in case a layer is provided on the surface of the silicon wafer as above, there is no pin hole and it is difficult to form the layer to a generally uniform thickness, which will also lower the yield.
The aforementioned troubles will arise not only in case the silicon wafer is used to form the head tips but in case the head tips in which the silicon-containing material such as a glass substrate is exposed are in contact with the ink, namely, in case the silicon-containing material is exposed in a channel in which alkaline ink flows.